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https://github.com/Kotlin/kotlinx.serialization

Kotlin multiplatform / multi-format serialization
https://github.com/Kotlin/kotlinx.serialization

cbor json kotlin protobuf serialization

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Kotlin multiplatform / multi-format serialization

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README 

        
# Kotlin multiplatform / multi-format reflectionless serialization



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[![Kotlin](https://img.shields.io/badge/kotlin-1.9.22-blue.svg?logo=kotlin)](http://kotlinlang.org)

[![Maven Central](https://img.shields.io/maven-central/v/org.jetbrains.kotlinx/kotlinx-serialization-core/1.6.3)](https://central.sonatype.com/artifact/org.jetbrains.kotlinx/kotlinx-serialization-core/1.6.3)

[![KDoc link](https://img.shields.io/badge/API_reference-KDoc-blue)](https://kotlinlang.org/api/kotlinx.serialization/)

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Kotlin serialization consists of a compiler plugin, that generates visitor code for serializable classes,

 runtime library with core serialization API and support libraries with various serialization formats.



* Supports Kotlin classes marked as `@Serializable` and standard collections.

* Provides [JSON](formats/README.md#JSON), [Protobuf](formats/README.md#ProtoBuf), [CBOR](formats/README.md#CBOR), [Hocon](formats/README.md#HOCON) and [Properties](formats/README.md#properties) formats.

* Complete multiplatform support: JVM, JS and Native.



## Table of contents



* [Introduction and references](#introduction-and-references)

* [Setup](#setup)

  * [Gradle](#gradle)

    * [1) Setting up the serialization plugin](#1-setting-up-the-serialization-plugin)

    * [2) Dependency on the JSON library](#2-dependency-on-the-json-library)

  * [Android](#android)

  * [Multiplatform (Common, JS, Native)](#multiplatform-common-js-native)

  * [Maven](#maven)

  * [Bazel](#bazel)



* **Additional links**

  * [Kotlin Serialization Guide](docs/serialization-guide.md)

  * [Full API reference](https://kotlinlang.org/api/kotlinx.serialization/)

  * [Submitting issues and PRs](CONTRIBUTING.md)

  * [Building this library](docs/building.md)



## Introduction and references



Here is a small example.



```kotlin

import kotlinx.serialization.*

import kotlinx.serialization.json.*



@Serializable 

data class Project(val name: String, val language: String)



fun main() {

    // Serializing objects

    val data = Project("kotlinx.serialization", "Kotlin")

    val string = Json.encodeToString(data)  

    println(string) // {"name":"kotlinx.serialization","language":"Kotlin"} 

    // Deserializing back into objects

    val obj = Json.decodeFromString(string)

    println(obj) // Project(name=kotlinx.serialization, language=Kotlin)

}

``` 



> You can get the full code [here](guide/example/example-readme-01.kt).



**Read the [Kotlin Serialization Guide](docs/serialization-guide.md) for all details.**



You can find auto-generated documentation website on [kotlinlang.org](https://kotlinlang.org/api/kotlinx.serialization/).



## Setup



[New versions](https://plugins.gradle.org/plugin/org.jetbrains.kotlin.plugin.serialization) of the serialization plugin are released in tandem with each new Kotlin compiler version.



Using Kotlin Serialization requires Kotlin compiler `1.4.0` or higher.

Make sure you have the corresponding Kotlin plugin installed in the IDE, no additional plugins for IDE are required.



### Gradle



To set up kotlinx.serialization, you have to do two things:

1) Add the **[serialization plugin](#1-setting-up-the-serialization-plugin)**.

2) Add the **[serialization library dependency](#2-dependency-on-the-json-library)**.



#### 1) Setting up the serialization plugin



You can set up the serialization plugin with the Kotlin plugin using the

[Gradle plugins DSL](https://docs.gradle.org/current/userguide/plugins.html#sec:plugins_block):



Kotlin DSL:



```kotlin

plugins {

    kotlin("jvm") version "1.9.22" // or kotlin("multiplatform") or any other kotlin plugin

    kotlin("plugin.serialization") version "1.9.22"

}

```       



Groovy DSL:



```gradle

plugins {

    id 'org.jetbrains.kotlin.multiplatform' version '1.9.22'

    id 'org.jetbrains.kotlin.plugin.serialization' version '1.9.22'

}

```



> Kotlin versions before 1.4.0 are not supported by the stable release of Kotlin serialization.



  Using apply plugin (the old way)



First, you have to add the serialization plugin to your classpath as the other [compiler plugins](https://kotlinlang.org/docs/reference/compiler-plugins.html):



Kotlin DSL:



```kotlin

buildscript {

    repositories { mavenCentral() }



    dependencies {

        val kotlinVersion = "1.9.22"

        classpath(kotlin("gradle-plugin", version = kotlinVersion))

        classpath(kotlin("serialization", version = kotlinVersion))

    }

}

```



Groovy DSL:



```gradle

buildscript {

    ext.kotlin_version = '1.9.22'

    repositories { mavenCentral() }



    dependencies {

        classpath "org.jetbrains.kotlin:kotlin-serialization:$kotlin_version"

    }

}

```



Then you can `apply plugin` (example in Groovy):



```gradle

apply plugin: 'kotlin' // or 'kotlin-multiplatform' for multiplatform projects

apply plugin: 'kotlinx-serialization'

```



#### 2) Dependency on the JSON library



After setting up the plugin, you have to add a dependency on the serialization library.

Note that while the plugin has version the same as the compiler one, runtime library has different coordinates, repository and versioning.



Kotlin DSL:



```kotlin

repositories {

    mavenCentral()

}



dependencies {

    implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.6.3")

}

```



Groovy DSL:



```gradle

repositories {

    mavenCentral()

}



dependencies {

    implementation "org.jetbrains.kotlinx:kotlinx-serialization-json:1.6.3"

}

```



>We also provide `kotlinx-serialization-core` artifact that contains all serialization API but does not have a bundled serialization format with it



### Android



By default, proguard rules are supplied with the library.

[These rules](rules/common.pro) keep serializers for _all_ serializable classes that are retained after shrinking,

so you don't need additional setup.



**However, these rules do not affect serializable classes if they have named companion objects.**



If you want to serialize classes with named companion objects, you need to add and edit rules below to your `proguard-rules.pro` configuration. 



Note that the rules for R8 differ depending on the [compatibility mode](https://r8.googlesource.com/r8/+/refs/heads/master/compatibility-faq.md) used.



Example of named companion rules for ProGuard and R8 compatibility mode



```proguard

# Serializer for classes with named companion objects are retrieved using `getDeclaredClasses`.

# If you have any, replace classes with those containing named companion objects.

-keepattributes InnerClasses # Needed for `getDeclaredClasses`.



-if @kotlinx.serialization.Serializable class

com.example.myapplication.HasNamedCompanion, # <-- List serializable classes with named companions.

com.example.myapplication.HasNamedCompanion2

{

    static **$* *;

}

-keepnames class <1>$$serializer { # -keepnames suffices; class is kept when serializer() is kept.

    static <1>$$serializer INSTANCE;

}

```



Example of named companion rules for R8 full mode



```proguard

# Serializer for classes with named companion objects are retrieved using `getDeclaredClasses`.

# If you have any, replace classes with those containing named companion objects.

-keepattributes InnerClasses # Needed for `getDeclaredClasses`.



-if @kotlinx.serialization.Serializable class

com.example.myapplication.HasNamedCompanion, # <-- List serializable classes with named companions.

com.example.myapplication.HasNamedCompanion2

{

    static **$* *;

}

-keepnames class <1>$$serializer { # -keepnames suffices; class is kept when serializer() is kept.

    static <1>$$serializer INSTANCE;

}



# Keep both serializer and serializable classes to save the attribute InnerClasses

-keepclasseswithmembers, allowshrinking, allowobfuscation, allowaccessmodification class

com.example.myapplication.HasNamedCompanion, # <-- List serializable classes with named companions.

com.example.myapplication.HasNamedCompanion2

{

    *;

}

```



In case you want to exclude serializable classes that are used, but never serialized at runtime,

you will need to write custom rules with narrower [class specifications](https://www.guardsquare.com/manual/configuration/usage).



### Multiplatform (Common, JS, Native)



Most of the modules are also available for Kotlin/JS and Kotlin/Native.

You can add dependency to the required module right to the common source set:

```gradle

commonMain {

    dependencies {

        // Works as common dependency as well as the platform one

        implementation "org.jetbrains.kotlinx:kotlinx-serialization-json:$serialization_version"

    }

}

```

The same artifact coordinates can be used to depend on platform-specific artifact in platform-specific source-set.



### Maven



Ensure the proper version of Kotlin and serialization version:



```xml



    1.9.22

    1.6.3



```



Add serialization plugin to Kotlin compiler plugin:



```xml



    

        

            org.jetbrains.kotlin

            kotlin-maven-plugin

            ${kotlin.version}

            

                

                    compile

                    compile

                    

                        compile

                    

                

            

            

                

                    kotlinx-serialization

                

            

            

                

                    org.jetbrains.kotlin

                    kotlin-maven-serialization

                    ${kotlin.version}

                

            

        

    



```



Add dependency on serialization runtime library:



```xml



    org.jetbrains.kotlinx

    kotlinx-serialization-json

    ${serialization.version}



```



### Bazel



To setup the Kotlin compiler plugin for Bazel, follow [the

example](https://github.com/bazelbuild/rules_kotlin/tree/master/examples/plugin/src/serialization)

from the `rules_kotlin` repository.